Hospitals such as St George’s, Queen Charlotte’s and Chelsea as well as Guy’s and St Thomas as well as others in Birmingham and Manchester are all taking part in the trial which is being rolled out in the coming months.

The trial has already begun at St George’s in the south of the capital. Nine hospitals in total in London are trialling the scheme.

Women booking in for maternity care are being asked to provide two forms of identification and a fuel bill or bank statement to prove their address.

BBC

Nigerian mother Priscilla who appeared on the BBC2 show

Women who are not entitled to free care will be asked to pay up front under the pilot scheme or agree to an instalment plan.

Computer software has been altered to allow staff to identify patients who are not eligible for NHS treatment and receptionists will be encouraged to record immigration status when people arrive.

Health chiefs have said though that pregnant women will not be turned away, although they have not ruled out that in the future they may be refused non-urgent care to those that will not pay.

‘Priscilla’ told the BBC2 programme Hospital: “If I have to work all my life, there is no way I can work for so much money.”

The NHS trust that manages the hospital said that it was pursuing payment but the hospital’s overseas visitor manager Terry Facey told the show that the debt was going to be “unmanageable” for her.

He added that while he had to try to enforce the rules it seemed “a bit fruitless at times”.

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The woman known simply as 'Priscilla' ran up an NHS bill of £500,000

Names of those who do not pay are passed on to the Home Office, who have the power to prevent them returning to the UK until the debt is paid off.

A spokesman for St George’s said: “We will not turn any women away or delay their maternity treatment if they cannot prove their identity, nor if they are not eligible for free care.

“Patients are entitled to free NHS care fi they live permanently and legally in Britain, which cannot usually be determined from passports or bills alone.”

Officials hope the scheme will be ruled out to more hospitals if the trial proves to be successful.

It has been estimated that overseas visitors using the NHS cost the health service around £500million annually.

Chief Executive of the Royal College of Midwives Cathy Warwick said that the move could deter women from seeking care in good time.

She said: “This might include women who are eligible for treatment but confused as to whether or not this is the case and ineligible women who are frightened that they will not be able to pay the bill in the longer term.”